(1) Field of the Invention
This invention relates to an improved process for preparing phenol by oxidizing benzene in the vapor phase with oxygen at an elevated temperature in the presence of a catalyst.
(2) Description of the Prior Art
Some proposals have been heretofore made to catalytically oxidize benzene in the vapor phase with oxygen at an elevated temperature in the absence of an alcohol to produce phenol. However, the yield of phenol produced by the heretofore proposed methods is very low, i.e., approximately 5%. For example, it is described in Japanese Laid-open Patent Application No. 61,439/73 to employ a catalyst substantially composed of copper phosphate and at least one metal oxide selected from iron oxide, manganese oxide, cobalt oxide and nickel oxide. The yields of phenol described therein are most 5.1%. Furthermore, it is described in Japanese Laid-open Patent Application No. 19,271/74 to employ a catalyst composed of copper borate. The yields of phenol described therein are at most 5.2%.
It also has been heretofore proposed to catalytically oxidize benzene in the vapor phase with oxygen at an elevated temperature in the presence of an alcohol to produce phenol. For example, it is described in British Pat. No. 1,274,653 that benzene is reacted in the vapor phase with oxygen in the presence of an alcohol at a temperature of 600.degree. to 700.degree. C. in a reactor having the internal surface coated with boric acid, thereby to produce phenol. The yield of phenol produced at a reaction temperature of 600.degree. C. is very low, i.e., approximately 3%. Even the highest yield of phenol is 10.5%, which was achieved at a reaction temperature of 640.degree. C. with a contact time of 4.0 seconds. Thus, it can be said that the catalytic oxidation carried out in the presence of an alcohol has some problems, namely, a high reaction temperature and/or a long contact time are necessary and the yields of phenol is still low.